Squirrel monkeys (Saimiri sciureus) are small, highly social and vocal New World primates. Much of the vocal activity of adults consists of rapid exchanges of one subtype of vocalization, the "chuck." Prior work in our laboratory has shown that chuck exchanges are engaged in preferentially by affiliative partners, are more common in females, and are acoustically individualistic. The individually distinctive features of chuck acoustic structure are presumably learned by group members, as playback studies have shown preferential responses to recorded chucks from group members but not to chucks of similar acoustic structure recorded from unfamiliar individuals. Juvenile squirrel monkeys also make chucks, but these achieve adult structure relatively late, around 18 months of age. We hypothesize that developing individuals learn the correct context from chuck production, as well as the acoustic details of the chucks of other group members, gradually. Since juvenile females spend more time in quiet affiliation with adult females, and juvenile males spend more time in social play, we hypothesize that females become more skillful than males in participating in the affiliative vocal subsystem as a result of greater learning opportunities. The robust nature of this vocal behavior, together with the evidence for an important role for individual experience, suggest that this vocal system has potential as a model system for studying the neurobiology of vocal learning in a nonhuman primate.